1. Field of the Invention.
The present invention relates to a magnetoresistive head for use in magnetic recording and playback devices, such as video tape recorders or digital audio tape recorders, so as to play back information recorded on a tapelike magnetic recording medium.
2. Description of the Related Art
Magnetic recording and playback devices, such as video tape-recorders or digital audio tape recorders, which use a magnetic tape as a recording medium, have been required to achieve a higher density and a larger capacity. Magnetoresistive heads have become applicable as playback magnetic heads which have a high sensitivity to detect signal magnetic fields and which are able to obtain a large playback output at high recording density.
FIGS. 10 to 13 show such a type of conventional magnetic recording head. In a magnetoresistive head 21, an arc-shaped medium-sliding surface 23, on which a magnetic tape slides, is formed at narrow end portions 22a of a pair of joined substrates 22 made of a nonmagnetic material. The leading ends of a magnetoresistive sensor layer 24 and marking layers 29 and 30 interposed between the substrates 22 are exposed at the medium-sliding surface 23.
When manufacturing the magnetoresistive head 21, as shown in FIG. 11, a lower gap layer (not shown) is formed on one of the substrates 22 with a lower shielding layer (not shown) therebetween, the magnetoresistive sensor layer 24 and a pair of bias layers 25 are formed on the lower gap layer, electrode layers 26 are respectively formed on the bias layers 25, and an upper shielding layer 27 is formed thereon, thereby forming a laminated member composed of the above layers. Then, three pairs of marking layers 28, 29, and 30 are formed on the upper shielding layer 27 so that they are symmetrical with respect to the magnetoresistive sensor layer 24 and so that they are offset with respect to one another.
Next, the substrates 22 are joined together so as to cover the laminated member, and are subjected to cutting so as to reduce the widths of the end portions 22a. As shown in FIG. 12 in a state in which the center of a belt-shaped lapping sheet 31 extending in the direction of arrow B (into the plane of the paper) is aligned with the center of the end portions 22a of the substrates 22 in the widthwise direction (the direction of arrow A) of the magnetoresistive sensor layer 24, the end portions 22a of the substrates 22 are lapped together with the laminated member while moving the lapping sheet 31 in the direction B. As a result, as shown in FIG. 13 the arc-shaped medium-sliding surface 23 is formed, and the leading end of the magnetoresistive sensor layer 24 is exposed at the top of the medium-sliding surface 23.
In this case, by performing lapping while observing the marking layers 28, 29, and 30 exposed at the end portions 22a of the substrates 22, a length H from the leading end to the rear end of the magnetoresistive sensor layer 24 can be adjusted to a predetermined value.
The conventional magnetoresistive head 21 thus configured and manufactured is assembled in a magnetic recording and playback device (not shown). The magnetoresistive head 21 is used in a state in which sensing current (steady-state current) is applied from the electrode layers 26 to the magnetoresistive sensor layer 24, and plays back information recorded on the magnetic tape, which slides on the medium-sliding surface 23, based on changes in resistance of the magnetoresistive sensor layer 24.
In the above-described conventional magnetoresistive head 21, however, by aligning the center of the lapping sheet 31 with the center of the end portions 22a of the substrates 22, the medium sliding surface 23 is arc-shaped so that the magnetic tape can smoothly slide thereon, and the leading end of the magnetoresistive sensor layer 24 is exposed at the top of the arc-shaped medium-sliding surface 23. When the end portions 22a of the substrates 22 vary in size in the widthwise direction (the direction A) of the magnetoresistive sensor layer 24 due to variations in working accuracy, as shown in FIG. 14, the leading end of the magnetoresistive sensor layer 24 is exposed at an offset position from the predetermined top of the arc-shaped medium-sliding surface 23. As a result, a spacing is likely to be formed between the magnetic tape sliding on the medium-sliding surface 23 and the leading end of the magnetoresistive sensor layer 24, and this may make it impossible to play back information recorded on the magnetic tape.
The present invention has been made in view of the above-described problems in the conventional art, and an object of the invention is to provide a magnetoresistive head in which a magnetoresistive sensor layer can be reliably exposed at a predetermined position of a medium-sliding surface so as to reliably play back information recorded on a magnetic tape and to provide a manufacturing method therefor.
In order to achieve the above object, according to an aspect of the present invention, there is provided a magnetoresistive head including a lower shielding layer, a magnetoresistive sensor layer formed on the lower shielding layer with a lower gap layer therebetween, and an upper shielding layer formed on the magnetoresistive sensor layer with an upper gap layer therebetween, wherein a marking layer is formed on at least one of the upper side of the upper shielding layer and the lower side of the lower shielding layer so as to be opposed to the magnetoresistive sensor layer, the leading ends of the magnetoresistive sensor layer and the marking layer are exposed at a medium-sliding surface on which a recording medium slides, a length of the leading end of the marking layer in the widthwise direction intersecting the direction of sliding of the recording medium is equal to a length from the leading end to the rear end of the magnetoresistive sensor layer, and the center in the widthwise direction of the marking layer is placed on a straight line that intersects the magnetoresistive sensor layer via the center thereof in the widthwise direction.
Since the medium-sliding surface can be formed in a state in which the center in the widthwise direction of a lapping sheet is aligned with the center in the widthwise direction of the magnetoresistive sensor layer, the leading end of the magnetoresistive sensor layer can be reliably exposed at a predetermined position on the medium-sliding surface, and information recorded on the recording medium can be played back reliably.
According to another aspect of the present invention, there is provided a magnetoresistive head including a lower shielding layer, a magnetoresistive sensor layer formed on the lower shielding layer with a lower gap layer therebetween, and an upper shielding layer formed on the magnetoresistive sensor layer with an upper gap layer therebetween, wherein a marking layer is formed on at least one of the upper side of the upper shielding layer and the lower side of the lower shielding layer so as to be opposed to the magnetoresistive sensor layer, the leading ends of the magnetoresistive sensor layer and the marking layer are exposed at a medium-sliding surface on which a recording medium slides, the marking layer is shaped so that a length thereof in the widthwise direction intersecting the direction of sliding of the recording medium changes at a fixed rate from the leading end toward the rear end, and a marker portion formed in the marking layer for detecting the center in the widthwise direction of the magnetoresistive sensor layer is placed on a straight line that intersects the magnetoresistive sensor layer via the center thereof in the widthwise direction.
Since the medium-sliding surface can be formed in a state in which the center in the widthwise direction of a lapping sheet is aligned with the center in the widthwise direction of the magnetoresistive sensor layer, the leading end of the magnetoresistive sensor layer can be reliably exposed at a predetermined position on the medium-sliding surface, and information recorded on the recording medium can be played back reliably.
Preferably, the marking layer is made of the same material as that of the upper and lower shielding layers and is directly formed on at least one of the upper and lower shielding layers.
This makes it possible to form the marking layer so as to be connected to the upper shielding layer and to form the lower shielding layer so as to be connected to the marking layer. This simplifies the process for manufacturing the magnetoresistive head.
According to a further aspect of the present invention, there is provided a magnetoresistive head manufacturing method including the steps of forming on a substrate a laminated member composed of a lower shielding layer, a lower gap layer, a magnetoresistive sensor layer, an upper gap layer, and an upper shielding layer stacked from the bottom in that order; forming, on at least one of the upper and lower surfaces of the laminated member, a marking layer which has a marker portion for detecting the center position in the widthwise direction of the magnetoresistive sensor layer as viewed from one end of the substrate and whose size in the widthwise direction changes at a fixed rate from the one end of the substrate toward the other end; and forming an arc-shaped medium-sliding surface on which a recording medium slides, by lapping the one end of the substrate together with the laminated member in a state in which the center in the widthwise direction of a lapping sheet with the center in the widthwise direction of the magnetoresistive sensor layer by using the marker portion, exposing the marking layer from the medium-sliding surface so that a length in the widthwise direction of the marking layer is equal to a predetermined value corresponding to a length from the leading end to the rear end of the magnetoresistive sensor layer, and thereby exposing the leading end of the magnetoresistive sensor layer at the top of the arc-shaped medium-sliding surface.
Since the center of the lapping sheet can be aligned with the center of the magnetoresistive sensor layer in the widthwise direction, the leading end of the magnetoresistive sensor layer can be reliably exposed at a predetermined position on the medium-sliding surface.
Preferably, the marking layer has a slot extending from the one end of the substrate toward the other end, and the slot serves as the marker portion.
Preferably, the marking layer is shaped like a right-angled triangle having a side which extends from the one end of the substrate toward the other end and passes through the center in the widthwise direction of the magnetoresistive sensor layer, and the side serves as the marker portion.
This makes it possible to form the marker portion easily.